The skin is subject to assault by a number of extrinsic and intrinsic factors. Extrinsic factors can include radiation, pollution, wind, heat and low humidity. Intrinsic factors include biochemical changes, and, for example, increased skin oil production. Any of these factors may result in visible deterioration of the skin's appearance. Excessive amounts of skin oil, or sebum, production may result in oily skin, a cosmetically unattractive and undesirable condition. There exists a continuing need, therefore, for improved skin protection and for reduction of the skin's oily appearance.
Many skin care actives are more effective at a low pH. For example, salicylic acid long has been recognized as an effective inhibitor of sebaceous gland activity and for other positive effects on the skin. Whereas salicylic acid may be formulated across a wide pH range, its effectiveness increases as the pH approaches 3.0 or below.
Dehydroacetic acid also has proven effective in improving skin texture and appearance, and has the additional benefit of reducing oily skin. See, for example, Biederman et al., U.S. Pat. No. 6,150,403. Attempts to formulate aqueous, low-pH skin care compositions containing dehydroacetic acid lead to the observation that the dehydroacetic acid begins to exhibit instability at a pH of below about 7.0. Therefore, a need remains for stable, low-pH skin care compositions to effect delivery of dehydroacetic acid, either alone or in combination with other low-pH skin care actives.